The invention concerns the connection of multiplexes lines connecting a time-division exchange to other time-division or electromechanical exchanges or to line concentrators to which a number of subscribers are connected. A time-division exchange transmits speech and signalling intelligence by means of pulse code modulation (PCM). The signals are contained in the time slots of a frame and carried by multiplex lines. Each multiplex signal originates at an exchange or line concentrator with its own ("distant") clock. The time-division exchange has its own ("local") clock. As is well known, the distant and local clocks are neither in phase not exactly synchronous, and the various exchanges use different types of signalling. In particular, the signalling used within and electromechanical exchange is different than that used within a time-division exchange. It is therefore necessary to synchronise the incoming multiplex signals with the local clock and to deal with the different signalling methods so as to be able to use the signalling intelligence for the various operations carried out by the time-division exchange which receives information over these incoming multiplex lines. Multiplex connection units for time-division exchanges are described in the article "Groupement d'equipements de synchronisation du systeme de commutation temporelle Platon" by D. FEUERSTEIN, J. B. JACOB, R. RENOULIN and J. GUEZOU, in the journal "Commutation et Electronique" No. 34, July 1971, pages 7 to 24.
In the connection units described, the signalling receiving and sending circuits differ, according to whether the multiplex lines connect the time-division exchange to other time-division exchanges, to electromechanical exchanges or to line concentrators, the signalling mode differing in each case.